1. Field of the Invention
The present invention relates to terrestrial digital multimedia broadcasting (DMB) service, and more particularly to a method and system for retransmitting an Internet protocol (IP) packet.
2. Description of the Related Art
Generally, in order to receive DMB service, a separate DMB receiver is required as it is not possible to receive a DMB signal through a general Internet Protocol (IP)-based wired/wireless network in which there is no DMB receiver. In order to enable DMB service to be provided through the general IP-based wired/wireless network, studies have been conducted in transmitting IP-encapsulating DMB data, which includes Motion Picture Expert Group-2 Transport Stream (MPEG-2 TS) and MPEG-4 Synchronization Layer (SL).
According to a retransmission system using a packet scheme for a DMB service developed through the studies, a terminal supporting the packet scheme without a separate DMB receiver can receive DMB data through a device having a DMB data decoding function and output DMB.
Hence, as described above, the user can be provided with terrestrial DMB service through a general terminal capable of accessing an IP network, even without a terrestrial DMB service-dedicated terminal. This enables the user to be provided with the terrestrial DMB service in an area where a terrestrial DMB base station is not installed, and in an area where it is not possible to receive DMB service because DMB signals are insufficient but it is possible to receive IP service.
FIG. 1 is a block diagram illustrating the configuration of a video multiplexer for terrestrial DMB. In the case of terrestrial DMB, video (MPEG-4 AVC), audio (MPEG-4 BSAC), and data information (Binary Format for Scene; BIFS) signals are packetized into a packetized elementary stream (PES), which is multiplexed together with Program Specific Information (PSI) to produce an MPEG-2 TS packet. In order to enhance the transmission quality of the signal packetized as described above, a frame error correction (FEC) signal is added to the packetized signal to produce a final video service stream, which is packetized according to Eureka-147 and transmitted.
In more detail, a video encoder 101 generating video data employs H.264/MPEG-4 Part 10 AVC (Advanced Video Coding) base profile level 1.3 for compression of a moving image, and an audio encoder 102 employs a bit-sliced arithmetic coding (BSAC) scheme included in MPEG-4 Part 3 for compression of audio which is accompanied by the video. Also, in the terrestrial DMB, a BIFS generator 103 employs a BIFS (Binary Format for Scenes) Core 2D graphic profile included in the MPEG-4 Part 1 system in order to provide a data broadcast function.
Each of Video data (ES), audio data (ES), and BIFS data information, which have been generated by the video encoder 101, the audio encoder 102, and the BIFS generator 103, is encapsulated into an MPEG-4 synchronization layer (SL) by an encapsulator 130. Thereafter, the video SL packet, audio SL packet, and BIFS SL packet are converted into an MPEG-2 TS through a PES packetizer 140 and a TS multiplexer 150, in which the PES packetizer 140 packetizes the video SL packet, audio SL packet, and BIFS SL packet to generate a PES packet according to the MPEG-2 standard, and the TS multiplexer 150 multiplexes the PES packet together with Program Specific Information (PSI) to produce an MPEG-2 TS packet.
According to the conventional method for converting a terrestrial DMB service stream of FIG. 1 into an IP packet, a TS packet generated through the PES packetizer 140 and TS multiplexer 150 is converted into an IP stream through an RTP/RTCP (Real-Time Transport Protocol/Real-Time Transport Control Protocol) packetizer 270 and a UDP/IP (User Datagram Protocol/Internet Protocol) packetizer 280, and then the IP stream is transmitted, as shown in FIG. 2. The RTP/RTCP contributes to packetization of multimedia signals, such as video and audio signals, so that the multimedia signals can be suitable for real-time transmission, and is widely used in an IPTV being currently provided. An FEC unit shown in FIG. 1 is used to provide a desired transmission quality because the reliability of a Digital Audio Broadcasting (DAB) network is poor. Such an FEC unit may be added also to the configuration of FIG. 2 if the reliability of a corresponding network is poor.
However, the conventional transmission method uses both MPEG-4 SL and MPEG-2 TS, as described above. These MPEG-4 SL and MPEG-2 TS have many duplicated functions, so the efficiency of the network may be degraded. The reason why the terrestrial DMB inefficiently uses duplicated functions in this way is that the SL layer must be used in order to synchronize video, audio, and data signals, compressed in MPEG-4, with each other, and additionally the MPEG-2 TS is used in view of its proven reliability.